The present invention relates to a method of counting particles suspended in a liquid medium, and more particulary to the above method suitable for use in an apparatus for counting blood cells in blood such as red blood cells and blood platelets so as to provide an indication of clogging conditions occurring in a liquid passage.
A method of automatically counting particles suspended in a liquid medium is used in a blood cell counter, and is classified into two typical methods, one of which utilizes changes in electric resistance due to particles, and the other uses scattered light from particles.
An example of a particle counting method based upon the detection of changes in electric resistance is disclosed in, for instance, U.S. Pat. No. 3,768,084. In this method, detector means having an aperture capable of passing a blood cell therethrough is used, and a pair of electrodes are disposed in the flow of a blood sample so that one electrode is on each side of the aperture, to cause an electric current to flow between the electrodes. When a blood cell passes through the aperture, the electric resistance between the electrodes varies pulsively. Not only the number of blood cells but also the size and volume of each blood cell can be known by measuring the state of resistance change.
A blood cell counting method based on the detection of scattered light is disclosed in, for example, a Japanese patent specification (Publication No. Sho. 51-24264 (1976)). In this method, a diluted blood sample passes through a flow cell in the state that the flow cell is irradiated with a thin light beam. When a blood cell passes through that portion of the flow cell which is irradiated with the thin light beam, light is scattered by the blood cell. Accordingly, the blood cell can be detected by measuring a change in the intensity of forward scattered light.
The above-mentioned two methods use a liquid passage system including the aperture or a small pipe serving as the flow cell, and therefore are encountered with a problem that the aperture or pipe may be clogged. Clogging readily takes place in the case where blood cells in a blood sample are agglutinated, and a great deal of labor is required to eliminate clogging.
Various measures have hitherto been taken to solve the clogging problem at the liquid passage system. For example, in the previously-referred U.S. Pat. No. 3,768,084, changes in electric resistance are detected to judge the presence or absence of aperture clogging. In more detail, when a large increase in resistance is detected continuously, it is judged that aperture clogging takes place, and an alarm is generated. However, such a method can detect aperture clogging only when an aperture is clogged to a remarkable extent, and can be used only in the particle counting method based upon the detection of changes in electric resistance.